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2· »• ' mounted in ordinary plug or cartridge breaker blows, it can be reset merely fuse cases.Fuses, while they provide protec- by returning the rheostat to off. The• operation of this type of cir- Motor Sentinel. It also can be used as Fig. 4 is a photograph of another thermal breaker, the Westinghouse tion, are one-time devices. Blow them, cuit Hreaker is shown in Fig. 3. The an on-off switch and is designed to and they have to be replaced. In a track power is supplied through the mount in a regular household-type circuit where shorts are rather fre- low-resistance winding of the relay. switch box. The little button marked quent (such as the power leads to the If the current draw is high enough to 1.0 is a replaceable heating element tracks), replacing fuses after each operate the relay (about 3 a. with a which determines the current rating. short circuit is not only inconvenient typical rotary relay), the relay oper- These units are available in 25 sizes but expensive. A circuit breaker is ates and cuts in the high-resistance from 0.5 a. to 14.3 a. This breaker must much more satisfactory. It will open winding. in series with the low. This cool down before being reset. a circuit on overload just like a fuse, immediately reduces the current and but ban be reset at will when the holds the relay open. Opening the vented by limiting the maximum cur- . trouble is cleared. Circuit breakers can be divided in- Current overloads may also be pre- circuit by turning the rheostat ofT rent which can flow. This is done by releases the relay. The additional con- using an ordinary tungsten-filament to two general classes: magnetic and tacts on the relay may be.used to op- lamp such as an automobile headlight thermal. Magnetic breakers are op- erate indicator lamps. erated by an electromagnet which quickly trips the breaker when the current reaches a predetermined point. Thermal breakers have a heating element to operate the breaker. Since it takes more time to heat an element than to build up magnetic force, a thermal breaker has a time lag similar to that described earlier for Fusetrons. Therefore, thermal breakers must have time to cool down before they can be reset, whereas a magnetic breaker can be immediately bulb. Lamps have a low resistance This type of circuit breaker can be when cool. This resistance rises rapidly as the lamp is heated. By placing a lamp in SELF RESETTING CIRCUIT BLZEAKER. 70 power Supply L= i \2• 0 reset. The author recommends magnetic-type circuit breakers for most model railroad purposes. Like fuses, the important rating of a circuit breaker is the current which operates it. The voltage rating is merely the maximum-voltage circuit in which it can be used. In other words, a 115 v. fuse can be used at any voltage less than 115, and the choice of the particular circuit breaker to be used is based on the current rating and the type. Fig. 2 shows four types of breakers: the Mini-Breaker; a small thermal unit; the Heinemann magnetic breaker; and a rotary relay. The Mini-Breaker is a thermal unit designed to replace a plug-type fuse. It costs approximately $1.50. The smaller breaker beside it is also resistance winding) - (both wndings. Red lead (low 1 -Ex Ira contacts To rail im meup 4 6211#Ells"i#'*0%21 Yellow lead t- 83ack lead common Connection) lill'•. • made from any relay which will operate on 12 v. and has enough space to allow a new heavy winding. The new winding should be made of wire no smaller than No. 18. The number of turns depends upon the relay itself, 11 2 j\(heret036 once w,nding) series with the circuit (Fig. 5), the maximum current flow is equal to the current of the lamp. In selecting a lamp for use as a the lamp is of less voltage than the power supply, of less voltage than the it will burn out; if more, the change in resistance not be enough to prevent overloads. The ordinary twin-filament 6 v. headlight bulb is satisfactory for 12 v. circuits provided both filaments are operated in will current limiter, it is necessary to use one whose rated voltage is equal to the voltage of the power .supply. If the lamp is series. The connection should be made to the two terminals on the base and not to the outer shell. Both filaments must be the same. A 21-21 candle power lamp will limit the current to about 3 a.; a 32-32 candle power lamp, about 4 a. and the current at which the relay should operate. Trial and error is the whose resistance remains uniformly best way of determining the correct low until the breaker or fuse operates, number of turns. If the relay buzzes a lamp increases its resistance as the when operated, change the connection current rises. Thus, it may interfere from one winding to the other. with control on heavy loads. For a thermal breaker-a very low-cost type, approximately 50 cents. This type should only be used when low cost is a necessity. The large, switch-type unit is a Heinemann magnetic breaker, which also comes with a slow-action device ' built in. It is designed to be used as i an on-off switch as well as a circuit 1 breaker. Switch-type breakers range in cost from $3 up. They are generally well constructed and the most reliable type. Where costs do not have to be held low, they are the type to use. To the right of the Heinemann breaker in Fig. 2 is a rotary relay such ; as is used for switch machines. It is also a useful self-resetting circuit j breaker. Cost is about $1.60. This is a particularly good type of circuit breaker for cab control, for once the '... ... . - August 1954 ... I .0•..3.• 9 )......4 z.... 1. :«·.-2 •i 042-7 ,•*'4,·. ..- g... -, Wt-'f, - ;S&79·"lf, *'4.'·:,t" :%-•.•fr#/:.: I k; 4' · I "•.2 A e:. 'J#..... t.. -.-/.It .'' T.::. :.1 ....9. 4 '-I.••'.61'...L*..T./- '....I.- 2.......... -, - .....1:- 1 '.. Fio. 2.·,-, . i i: '; ·44-Il- + - -- - .--«. - -». . 41 ,..:..:./. 4 ...=963 -: .) 7/.747: . - i ...........*· . t.. S'....5.«t,».1 --' 2 -. 46/. s ..• <••).r . + .... -.....*. ..:i.&: = .....,# I ..21: I. .../ ¥ *41.I'. .... ..--Unlike circuit breakers or fuses,